Ragone plots revisited: A review of methodology and application across energy storage technologies

The term “Ragone plot” refers to a popular and helpful comparison framework that quantifies the energy–power relationship of an energy storage material, device, or system. While there is consensus on the general Ragone plot concept, many implementations are found in the literature. This article provides a systematic and comprehensive review of the Ragone plot methodology in the field of electric energy storage. A faceted taxonomy is developed, enabling existing and future Ragone plots to be unambiguously classified and contextualized. This review focuses on disseminating the methodology, discussing technology-specific aspects, and giving an overview of the further sizing and design methods developed based on Ragone plots. Additionally, this article identifies best practices for obtaining and presenting Ragone plots. This review is not limited to electrochemical energy storage, where the framework is traditionally applied, but also encompasses all other electric energy storage. Here, the Ragone plot can compactly quantify off-design performance and operational flexibility, independent of technology-specific performance indicators. This review is the first of its kind and can, therefore, guide future application of the Ragone plot framework in a consistent manner.